struct TrieNode
{
    string word;
    unordered_map<char,TrieNode *> children;
    TrieNode()
    {
        this->word = "";
    }   
};

void insertTrie(TrieNode * root,const string & word)
{
    TrieNode * node = root;
    for (auto e : word)
    {
        if (!node->children.count(e))
        {
            node->children[e] = new TrieNode();
        }
        node = node->children[e];
    }
    node->word = word;
}

class Solution {
public:
    vector<string> findWords(vector<vector<char>> & board, vector<string> & words) {
        TrieNode * root = new TrieNode();
        set<string> res;
        vector<string> ans;
        for (auto& e : words)
        {
            insertTrie(root, e);
        }
        for (int i = 0; i < board.size(); ++i)
        {
            for (int j = 0; j < board[0].size(); ++j)
            {
                dfs(board, i, j, root, res);
            }
        }        
        for (auto& e : res)
        {
            ans.emplace_back(e);
        }
        return ans;        
    }

    int dirs[4][2] = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
    bool dfs(vector<vector<char>>& board, int x, int y, TrieNode * root, set<string> & res)
    {
        char ch = board[x][y];        
        if (!root->children.count(ch))
        {
            return false;
        }
        root = root->children[ch];
        if (root->word.size() > 0)
        {
            res.insert(root->word);
        }

        board[x][y] = '#';
        for (int i = 0; i < 4; ++i)
        {
            int nx = x + dirs[i][0];
            int ny = y + dirs[i][1];
            if (nx >= 0 && nx < board.size() && ny >= 0 && ny < board[0].size())
            {
                if (board[nx][ny] != '#')
                {
                    dfs(board, nx, ny, root,res);
                }
            }
        }
        board[x][y] = ch;
        return true;      
    }
};